Before divining their holy prophecies, the priestesses of the Oracle of Delphi — set high on Greece’s Mount Parnassus — inhaled a ”strange, sweet odor” said to rise from a chasm in the temple’s floor. Yet when Delphi was excavated at the end of the 19th century, no such chasm was found, and the Oracle was dismissed as a hoax. New York Times writer William J. Broad shows how two scientists working at Delphi now believe that the hallucinogen in question may have been ethylene, contained in petrochemical gasses seeping up from beneath the temple. Sound far-fetched? Maybe it is. But in Broad’s capable hands, this is only a piece of an absorbing historical tale.